The constant movement of the tide around the coast results in the growth of shifting mounds and ridges on the seabed. The approach to a port is often by way of an estuary, and the extra sand and mud washed down by a river builds up further obstacles for shipping.
|Sevenstones lightvessel. © NMM|
Building a fixed beacon on this shifting material is often impossible. Lightships are the best choice for sites like these. This photograph is of the Sevenstones lightvessel.
Lightvessels are not designed for travel and often have no engines for propulsion. They are designed to be moored in the open sea, whatever the weather conditions.
This image from 1882 shows the Galloper Lightship in a gale. If, for any reason, a lightship breaks adrift, it must put out its light and then be re-anchored as soon as possible with its spare anchor.
|Galloper Lightship. © NMM|
|Calshot Lightship off Southampton Water. © NMM|
Ocean-going vessels rely on lightships being in the exact location marked on their sea charts. The navigational calculations of a ship become unreliable and dangerous if the lightship has moved. This photograph of the Calshot Lightship, off Southampton Water, was taken in the 1900s.
Trinity House's first lightvessel - the first in the world - was moored near Nore Sands at the mouth of the Thames in 1732. It was closely followed by the Goodwin Lightship in 1793.
|The Nore Lightship. © NMM|
|The Goodwin Lightship. © NMM|
These early craft were small, wooden ships, often Dutch galliots bought especially for conversion to lightvessels. By 1819 there were nine lightvessels in England.
The first lights were candle powered or used oil lamps that burned sperm whale oil. Some of the early ships were fitted with sails in case they broke adrift.
By the beginning of the 20th century it was usual for a Trinity House lightvessel to have a crew of 11. This consisted of a master and six ratings on board, and a master and three ratings ashore.
The masters were changed every month, while the rest of the crew served a month afloat followed by two weeks of shore leave. The crews were qualified seamen who had normally served at least two years on deck.
When a man started he would serve as a general seaman before being promoted to Fog Signal Driver and Lamplighter. After 15 to 20 years of service, he could become a master. This image is of the crew of the South Goodwin Lightship.
|Crew of the South Goodwin Lightship. © NMM|
Today, Trinity House's lightvessels are all automated. The last manned ship was the Dowsing Lightship, shown in this photograph. She was located 75 km (45 miles) north of Cromer and 75 km (45 miles) north-east of Mablethorpe.
|Dowsing Lightship. © NMM|
The Dowsing Lightship was built by Phillip and Son of Dartmouth in 1958. She had a helicopter pad, which was used to bring in supplies and new crew members.
|Relieving the Tongue Lightship by night. © NMM|
Before helicopters were used, lightships were re-equipped by a fleet of Trinity House supply ships.
This 1882 picture shows a supply ship relieving the Tongue Lightship during the night. Ships such as this would land provisions and bring replacement crews to relieve the staff of the lightship.